Rechargeable power storage devices, such as lead-acid batteries, lithium-ion batteries and super capacitors, have been widely used in portable devices, industrial applications, hybrid and electric vehicles and other fields. For these power storage devices, the voltage is limited, such as the voltage of lithium-ion battery is about in the range of 3V˜4.3V, and the voltage of the super capacitor is usually not more than 2.7V.
In order to meet the application requirements of high voltage applications in practical applications, the high storage voltage of these power storage devices is usually obtained by connecting a plurality of power storage devices in series. However, during the charging and discharging of the plurality of power storage devices in series, the voltage imbalance of the respective power storage devices may occur, taking the power storage device as the battery for an example, in the charging phase, each battery in series is like a voltage divider, because the different battery capacity and/or battery leakage, the battery voltage will be imbalanced. Specifically, a battery with a smaller electrical capacity will be subjected to greater voltage stress and the battery will be damaged if the voltage stress exceeds the maximum voltage that the battery can withstand. Therefore, for a plurality of power storage devices connected in series, the voltage equalization between the power storage units is very important.
In the prior art, the voltage equalization of each power storage unit is realized by discharging the power storage unit having a higher voltage to the resistance. However, this method has some drawbacks, that is, the power of high-voltage power storage device consumed in the discharge resistance causes additional power loss. At present, in order to overcome the technical drawbacks of the above-mentioned voltage equalization method which can cause power loss, a method of voltage equalization of non-dissipative active batteries is proposed in the prior art, such as by using a flyback power conversion technology or bidirectional buck-boost power conversion technology to achieve equalization of the voltage equalization circuit. Although, in these methods, it is not necessary to consume power in a discharge resistance; however, battery-balanced circuits based on flyback power converters or bidirectional buck-boost power converters contain bulky magnetic components that can result in larger and higher cost of balanced circuits.
Further, in order to reduce the circuit volume of the equalization system and to reduce the cost of consumption, in the related patents (such as U.S. Pat. No. 5,710,504), an automatic battery voltage equalization system based on switched capacitor technology is proposed. As shown in FIG. 1, a battery voltage equalization circuit based on the switching capacitor is provided by the patent, and is used to equalize the voltage of n battery cells (Cell1˜Celln) in series. In the equalization circuit of FIG. 1, it comprises n single-pole double-throw switches (S1˜Sn, n is an integer greater than or equal to 1), n−1 capacitors (C1˜Cn−1) and a control unit; wherein, the two static terminals of any switch of the n single-pole double-throw switches are respectively connected to the positive electrode and the negative electrode of a corresponding battery unit; the selecting terminals of each two adjacent switches of the n single-pole double-throw switches are connected through a corresponding capacitor; the control unit is used to control the n single-pole double-throw switches to be switched off. As can be seen from FIG. 1, the bulky magnetic components are not provided in the battery voltage equalization circuit, reducing the circuit volume and cost consumption of the equalization system. However, this voltage equalization circuit provides only a charge transfer path between adjacent cell cells in a plurality of series cells. For the entire voltage equalization system circuit, the voltage equalization speed is limited. Then when the number of batteries in series is relatively large, through this voltage equalization circuit, it takes a lot of time to achieve the voltage balance between the battery cells. It can be seen that there is still a technical problem that the voltage equalization circuit based on the switched capacitor has a low voltage equalization speed and are not suitable to the voltage equalization of the large number of power storage unit series links.